1. Field of the Invention
The present invention relates to a fuel injection system capable of supplying unburned gas such as hydrocarbon (HC) into exhaust gas of an engine.
2. Description of Related Art
There has been a known fuel injection system for supplying unburned gas into exhaust gas of an engine in order to regenerate a particulate filter disposed in an exhaust passage or in order to quickly heat a catalyst disposed in the exhaust passage. A technology of performing a post-injection after a normal injection is known as means for supplying the unburned gas into the exhaust gas of the engine. For instance, the normal injection is a single injection consisting of a main injection or is a multi-injection as a combination of a pilot injection and the main injection. The normal injection is performed to generate engine torque. For instance, the post-injection is performed at a crank angle of 20–50° (20–50° CA) after a top dead center.
In the post-injection, fuel is supplied during an expansion stroke of the engine. Therefore, combustion becomes unstable and a large amount of the unburned gas (HC) is generated. The unburned gas is ignited in the particulate filter or the catalyst disposed in the exhaust passage, and regenerates the particulate filter or quickly heats the catalyst.
A control device for controlling injectors includes injection controlling means and injector driving means. The injection controlling means is a part of a function of an electronic control unit (ECU). The injector driving means is a part of a function of an electric drive unit (EDU), or an injector drive circuit. The injection controlling means calculates an injection pattern, injection timing, and an injection quantity or an injection period corresponding to an operating state of the engine, and outputs command signals (injector driving signals) for each injection. The injector driving means supplies driving power to an actuator (an electromagnetic valve, for instance) of the injector responsive to the command signal, which is outputted from the ECU.
Since the injector driving means is a circuit for supplying a driving current to the injector for each injection, the injector driving means generates a large amount of heat. Therefore, suppression of the heat generation of the injector driving means is required. Specifically, in the case of the multi-injection for performing the multiple fuel injections during one compression stroke, the number of times of the injections is large, so a large amount of heat is generated.
Moreover, the number of times of the injections shows a positive correlation with engine rotation speed. Therefore, the amount of the heat generated by the injector drive circuit shows a positive correlation with the engine rotation speed. Accordingly, the amount of the heat generated by the injector drive circuit increases as the engine rotation speed increases. In some cases, an upper limit of the engine rotation speed is set by the heat generation limit of the injector drive circuit.
When the post-injection is performed in a situation where the suppression of the heat generation of the injector drive circuit is highly required, suppression of the heat generation due to the post-injection is required in addition to the suppression of the heat generation due to the normal injection. Therefore, it is required to suppress the heat generation of the injector drive circuit specifically in a period for performing the post-injection.
A technology for suspending the injection if the operating state of the engine is in a certain area where the engine rotation speed is high and a load on the engine is light is known as a technology for suppressing the heat generation of the injector driving means as disclosed in Unexamined Japanese Patent Application Publication No. H09-060541, for instance. A technology for suspending the injection if a common rail pressure is higher than a target value by a predetermined value or more when the engine reaches an accelerating state is known as a technology for suppressing the heat generation of the injector driving means as disclosed in Unexamined Japanese Patent Application Publication No. H08-232740, for instance.
However, the above technologies are performed under the conditions quite different from the condition for performing the post-injection. Therefore, the technologies cannot suppress the heat generation of the injector drive circuit in the period for performing the post-injection.